Apparatus for making compacted pellets of solid phase carbon dioxide

ABSTRACT

Apparatus for making compacted pellets of solid phase carbon dioxide comprises die means having radial extrusion passages therein, injector means for forming snow from liquid carbon dioxide flashed into an expansion zone adjacent the inlet end of said extrusion passages, compression means for compacting said snow and extruding the same outwardly through said passages to form elongated, rod-like extrusions of solid phase carbon dioxide, and back pressure means for exerting contact pressure against said extrusions leaving the outer ends of said passages in said die means. A novel method in accordance with the present invention comprises the formation of compacted pellets of solid phase carbon dioxide from liquid phase carbon dioxide to form snow, compressing said snow to force the same through an extrusion passageway forming elongated, rod-like extrusions of compacted solid phase carbon dioxide and exerting back pressure against the rod-like extrusion as they leave the passageways thereby stabilizing the extrusions permitting the escape of gas without fracturing the same.

United States Paten 1191 Cann [ Jan. 22, 1974 {75] Inventor: Lyle L.Cann, Peotone, Ill.

[73] Assignee: Chemetror Corporation, Chicago,

Ill.

22 Filed: Aug. 28, 1972 21 Appl. No.: 284,264

52 us. or 62/35, 62/10, 425/382 51 Int. Cl. B29 3/00 581 Field ofSearch.. 62/10, 35; 425/331, 382, 462; 264/140, 141

[56] References Cited UNITED STATES PATENTS 1,919,698 7/1933 l-lessling425/382 2,252,900 8/1941 Shater 425/331 X 3,576,112 4/1971 Frost et a162/10 3,660,986 5/1972 l-lardt et al 62/10 FOREIGN PATENTS ORAPPLICATIONS 484,570 10/1929 Germany 62/35 477,587 12/1937 Great Britain62/35 477,834 12/1937 Great Britain 62/35 Primary Examiner-R. SpencerAnnear Attorney, Agent, or FirmRichard D. Mason et al.

p [57] ABSTRACT Apparatus for making compacted pellets of solid phasecarbon dioxide comprises die means having radial extrusion passagestherein, injector means for forming snow from liquid carbon dioxideflashed into an expansion zone adjacent the inlet end of said extrusionpassages, compression means for compacting said snow and extruding thesame outwardly through said passages to form elongated, rod-likeextrusions of solid phase carbon dioxide, and back pressure means forexerting contact pressure against said extrusions leaving the outer endsof said passages in said die means.

A novel method in accordance with the present invention comprises theformation of compacted pellets of solid phase carbon dioxide from liquidphase carbon dioxide to form snow, compressing said snow to force thesame through an extrusion passageway forming elongated, rod-likeextrusions of compacted solid phase carbon dioxide and exerting backpressure against the rod-like extrusion as they leave the passagewaysthereby stabilizing the extrusions permitting the escape of gas withoutfracturing the same.

19 Claims, 7 Drawing Figures PATENTEDJANZPWM 3.786.6d5

sum 1 er a IIB APPARATUS FOR MAKING COMPACTED PELLETS OF SOLID PHASECARBON DIOXIDE The present invention relates to a new and improvedmethod and apparatus for making compacted pellets of solid'phase carbondioxide. More particularly, the carbon dioxide pellets produced inaccordance with the present invention are ideally suitable for many andvaried uses including fast freezing and other cold packaging of foodstuffs wherein the pellets are mixed directly with the food, saidpellets eventually sublimating into gaseous carbon dioxide.

In the past, solid phase carbon dioxide pellets have been produced byflashing liquid carbon dioxide to form snow and subsequently compactingthe snow by a ram or other means into extrusion passages to formcompacted solid phase carbon dioxide extrusions. One problem associatedwith forming solid phase carbon dioxide extrusions at high productionrates in this manner has been the tendency of the newly formedextrusions leaving the extrusion passages to become unstable physicallybecause of gaseous carbon dioxide entrapped internally of the extrudedform. Carbon dioxide is a substance having a triple point wherein solid,liquid and gaseous forms can exist at the same temperature and pressureconditions. When the liquid is flashed to snow (solid phase) some of theliquid also goes into gaseous form. When the snow is compacted this gasmay become entrapped internally within the rod-like extrusions and asthe extrusions emerge the gas expands causing the extruded material torupture.

The present invention provides a new and improved method and apparatusfor use in forming compacted pellets of solid phase carbon dioxide.

It is therefore an object of the invention to provide a new and improvedmethod and apparatus of the character described wherein rod-likeextrusions of solid phase carbon dioxide are formed to provide suchpellets.

Another object of the present invention is to provide a new and improvedapparatus of the character described having means for removing andcarrying away gaseous carbon dioxide formed during the flashing ofliquid carbon dioxide into snow.

' Another object of the present invention is to provide a new andimproved apparatus of the character described having means therein forclosing the outer ends of said extrusion passages during the initialstages of operation until sufficient solid'phase material is present inthe extrusion passages to make continuous rod-like extrusions.

Another object of the present invention is to provide a novel apparatusof the character described wherein said rod-like extrusions of solidphase carbon dioxide leaving the extrusion passages are subjected todirect contact or back pressure for reducing the tendency of saidextrusions to rupture because of gaseous carbon dioxide entrapped withinthe interior of the extrusions.

Another object of the present invention is to provide a new and improvedextrusion apparatus having a novel structuredefining an expansionchamber, extrusion die and impeller therein movable around said chamberto form an orbital moving compression zone for compacting and extrudingcarbon dioxide snow into solid phaserod-like extrusions.

Another object of theinvention is to provide a new and improvedextrusion apparatus for making compacted pellets of carbon dioxide snowin an extremely efficient manner.

Another object of the present invention is to provide a new and improvedextrusion apparatus wherein a moving expansion zone is provided forflashing liquid carbondioxide into snow in synchronous relation to theorbiting movement of an eccentric impeller which forms a movingcompression zone for compacting and extruding the snow outwardly intosolid phase carbon dioxide rod-like extrusions.

Another objective of the present invention is to provide a novel carbondioxide extrusion apparatus which is compact in physical size yetcapable of producing a high volume flow rate of solid phase extrusions.

Another object of the invention is to provide a new and improvedextrusion apparatus of the character described which does not require asnow horn.

These and other objects and advantages of the present invention areaccomplished by a new and improved .method of forming compacted pelletsof solid phase carbon dioxide from liquid carbon dioxide generallycomprising the steps of flashing the liquid to form snow, compacting thesnow and extruding the material through a confining passageway to formrod-like extrusions and exerting contact pressure against saidextrusions as they emerge from the outer end of the extrusionpassageways.

A novel apparatus in accordance with the invention generally includes anannular die having a plurality of radial extrusion passages therein andinjector means for flashing liquid carbon dioxide to form snow withinthe die immediately ahead of and behind a compression zone formed by aneccentric impeller mounted for movement around the die. The orbitingimpeller and die form a moving compression zone for compacting andextruding the snow outwardly through the extrusion passages and formingelongated rod-like extrusions of solid phase carbon dioxide. Backpressure means is provided for exerting direct contact pressure againstthe rod-like extrusions exiting the outer end of the extrusion passagessuch that the extruded material has little if any tendency to rupture ordisintegrate as gas in the interior of the extrusion escapes intoambient pressure and temperature conditions outside the extrusion diepassages.

The rod-like extrusions break off under their own weight after leavingthe extrusion passages or may be broken off by a deflector to formpellets of a desired maximum length. The pellets are somewhat porousrather than clear solid ice and have excellent heat transfercharacteristics for many and varied uses including the cooling of foodstuffs and the like mixed therewith.

For a better understanding of the invention, reference should be had tothe following detailed description taken in conjunction with thedrawings, in which:

FIG. I is a side elevational view of a new and improved apparatus formaking dry ice pellets constructed in accordance with the features ofthe present invention;

FIG. 2 is a fragmentary, vertical cross sectional view takensubstantially along lines 2-2 of FIG. 6;

FIG. 5 is a fragmentary, horizontal, cross sectional view takensubstantially along lines 5-5 of FIG. 2;

FIG. 6 is a horizontal, cross sectional view taken substantially alonglines 66 of FIG. 2; and

FIG. 7 is an exploded perspective view of an extrusion spring assemblyin accordance with the features of the present invention.

Referring now more particularly to the drawings, therein is illustrateda new and improved apparatus for making compacted pellets of solid phasecarbon dioxide constructed in accordance with the features of thepresent invention and referred to generally by the reference numeral 10.The apparatus 10 includes an extrusion apparatus 12 driven by anddirectly coupled to the vertical output shaft (not shown) of a gearreducer 14 which is driven by an electrical motor or other prime mover16. The motor includes a rotor shaft 18 which is directly coupled to theinput shaft 20 of the gear reducer 14 by a coupling 22. The gear reducerl4 and motor 16 are mounted on the upper surface of a base plate 24 andthe extrusion apparatus 12 of the pellet machine is supported from theunderside of the base plate in direct coaxial alignment with the outputshaft of the gear reducer 14.

Carbon dioxide in liquified form is provided under pressure to theextrusion apparatus 12 from a suitable source of supply through an inputor supply line 26 and vaporous carbon dioxide or exhaust gas formedduring the extrusion process in the apparatus is vented from theextrusion apparatus via a pair of vapor exhaust conduits 28.

In accordance with the present invention the extrusion apparatus 12includes an annular extrusion chamber 30 (FIGS. 2, 3 and 4)concentrically aligned with a vertical axis 32, which axis extendsthrough and is coaxially aligned with the output shaft (not shown) ofthe gear reducer I4. The annular extrusion chamber includes an annularwall formed by a plurality of circular die rings 34, 36 and 38 securedtogether by a plurality of circumferentially spaced apart bolts 40. Eachdie ring 34, 36 and 38 is provided with a plurality of vertical passages42 aligned with matching passages in the other rings when the rings areassembled together to form the extrusion chamber as shown best in FIGS.2

- and 4. The vertical passages 42 are spaced equidistant around the dierings and as shown in FIG. 3, the passages 42 may be spacedapproximately apart so that a total of 24 passages are provided. Thenumber of passages required may be increased or decreased depending uponthe size or diameter of the die rings and the mechanical strength of thematerials used. One pair of passages 42a in the rings 34 and 38 are ofreduced diameter and are spaced approximately 30 on opposite sides ofanother passage 42!) in the ring 38, also of reduced diameter. Thepassage 42b is one of four such passages that are spaced 90 apart (asshown in FIG. 3) for use in injecting fluid into the chamber 30. One ofthe reduced diameter passages 42a is used for passing liquid carbondioxide downwardly to the valving mechanism of the extrusion apparatus12 and all of the four, quadrantally spaced, reduced diameter passages42b are used for the distribution of carbon dioxide liquid from thevalving mechanism to expansion nozzles in the extrusion chamber 30. Someof the remaining, larger diameter passages 42 spaced around and betweenthe passages 42a and 42b are used to accommodate bolts 40 for holdingthe rings 34, 36 and 38 together and the other remaining passages 42 areused for the exhaust system to handle carbon dioxide vapor as will bedescribed hereinafter.

The rings 34 and 38 are provided with a plurality of horizontal,radially extending extrusion passages 44, spaced between the verticalpassages 42 on the respective lower and upper surfaces. The extrusionpassages communicate between a cylindrical inside vertical die wallsurface 46 and a concentric outside vertical die wall surface 48 (asbest shown in FIGS. 3 and 4). The central or middle die ring 36 includesa plurality of matching, horizontal, radially extending extrusionpassages 50 on its upper and lower surfaces. The passages 50 on themiddle die ring align with facing passages 44 on the upper and lower dierings 34 and 38 to form pairs of vertically spaced apart, horizontallyextending, elongated extrusion passageways 52. The passages extendradially outwardly from the annular extrusion chamber 30 between theinside and outside wall surfaces 46 and 48 of the rings 34 and 38. Themiddle die ring 36 includes a cylindrical inside wall surface 54 alignedwith the inside wall surfaces 46 of the upper and lower die rings 34 and36 to form a generally cylindrical, peripheral wall surface defining theannular extrusion chamber 30.

The middle die ring 36 includes an outwardly extending annular flangeportion 56 having a vertical thickness greater than the thickness orspacing between the upper and lower surfaces of the middle ring whichengage the facing surfaces of the upper and lower rings 34 and 38. Theouter flange 56 on the middle die ring 36 is formed with a plurality ofpairs of vertically aligned spaced apart upper and lowercircumferentially spaced, inwardly extending radial pockets 58. Eachpocket 58 includes an inner, vertical wall surface 60 in communicationwith the outer end of a pair of adjacent, horizontal extrusion passages52 as best shown in FIG. 3. The inner pocket surfaces 60 are alignedwith the outer cylindrical wall surfaces 48 of the upper and lower dierings 34 and 38, and the outer open ends of the pairs of horizontalextrusion passages 52 are spaced at opposite ends of the inner pocketsurfaces 60 between radially outwardly extending opposing pocket endsurfaces 62 (FIG. 3). Each pocket 58 also includes a horizontal basesurface 64 and the annular flange portion 56 of the middle die ring 36,provides a continuous middle portion 66 between the rows of upper andlower pockets 58. The pockets are spaced between solid, radial segments68 and these segments project upwardly and downwardly from therespective base surfaces 64 of the pockets as best shown in FIG. 7. Theupper ends of the upwardly facing ring of pockets and the lower ends ofthe downwardly facing ring of pockets are closed by a pair of annularwasher-like ring members 70 secured to the upper and lower surfaces ofthe segments 68 by means of bolt and nut assemblies 72 as best shown inFIG. 4.

From the foregoing it will be seen that the extrusion passages 52 extendradially outward of the annular extrusion chamber 30 through the dierings 34, 36 and 38 and that pairs of adjacent horizontal passagesterminate adjacent the opposite ends of the inner surfaces 60 of thespaced apart upper and lower outwardly opening pockets 58 formed in themiddle flange portion 56 of the middle die ring 36.

As best shown in FIGS. 3, 4 and 7 each extrusion passages 52 is formedby a pair of cooperating passage surfaces 44 and 50 when the upper andlower die rings 34 and 38 are assembled with the middle die ring 36. Thepassages are formed with an enlarged, frusto-conically tapered entry orinlet end portion 53 (FIG. 3) for compacting the carbon dioxide snow asit is forced outwardly. The frusto-conically shaped inlet portion 53 ofeach passage is tapered at an angle of approximately with respect to theradial axis of the passage to provide a convergent effect on the snow asit is extruded outwardly. Outwardly of the inlet or entry portion ofeach passage, the passage wall is tapered at a much smaller angle in theorder of 3 to 5. The outer, gently tapered portion of the passages 52are substantially longer than the entry portion and the passages reach aminimum dimension at the outer end adjacent the inner surfaces 60 of thepockets 58.

As best shown in FIGS. 3 and 4, the shanks of the bolts 72 arepositioned to project vertically through the center of each pocket 58and, in accordance with the present invention, the bolts serve ascentering pins for generally cylindrical spools 74 used for supportingthe central bight portions of pairs of U-shaped, back pressure, contactsprings 76 (FIGS. 3 and 7). Each spring 76 includes freely deflectableopposite outer ends, which in the nondeflected state as shown in FIG. 3,project outwardly towards and contact opposing radial side surfaces 62of the pockets 58. The springs 76 are formed of spring material of thedesired thickness, strength and resiliency in order to resist theoutward movement of the rod-like extrusions of solid phase carbondioxide material exiting the outer ends of the extrusion passages 52.

In one prototype device in accordance with the invention the springs 76were formed of commercially available, blue tempered, spring steelstrip. The spring material was 0.025 inch in thickness, /2 inch widewith rounded edges'and was cut to length from a continuous stock stripand bent to shape and notched without requiring further heat treatment.Bending of the spring material into the illustrated U-shapeconfiguration was accomplished on a press brake and the bending angleand length of the spring strip is chosen to provide a positive bias ofthe outer free ends of the springs against the side surfaces 62 ofapproximately 2 lbs. measured at the tips of the springs when insertedand secured in place in the pockets 58 when the springs are deflected asduring the making of extrusions, the springsexert a force ofapproximately 23 lbs. measured at the tips. It

has been found that a pair of springs 76 sandwiched together as shown inFIGS. 3 and 7 and mounted in each pocket is effective to produce highquality extrusions.

The middle or bight portion of each pair of springs 76 is maintained ina radially centered position within a pocket 58 by means of a centeringpin 78 which is mounted in an aligned vertical passage provided in themiddle portion 66 of the die ring 36. The bight portions of the upperand lower pairs of U-shaped springs 76 are formed with vertical notches76a on the lower and upper edges respectively (FIG. 7), at the center sothat the springs are seated and maintained by the upper and lower endsof the pins 78 in a centered disposition relative to each pair ofextrusion passages 52 within a pocket 58. As shown in FIG. 3 each pairof springs is free to pivot about a vertical center axis as maintainedby the notches 76a in the springs seated on the pin 78 and the springpairs are backed up by the generally cylindrical support spools 74.

Initially, as the solid phase carbon dioxide snow is compacted andextruded through the tapered passages 52 it is resisted essentially onlyby the frictional forces of the passage walls. The outer deflectable endportions of the springs 76 act to retain this material in the form of anoutwardly projecting, rod-like slug or extrusion until sufficient backpressure is built up in the extruded material formed in the extrusionpassages 52. Without the springs 76 initially to begin the extrusionprocess, the material would simply pass out the open outer ends of thepassages 52 without sufficient compaction to form pellets. The springs76 thus facilitate the startup of the extrusion process. In addition,while maintaining back pressure on the extrusions, the springs permitvaporous carbon dioxide that emanates from within the extrusion passagesto be exhausted as the extrusions reach the outer end of the passages.

The compacted snow also contains gaseous carbon dioxide. As the snow iscompacted and extruded through the passages 52 to form elongated,cylindrical rod-like extrusions, the gas within the interior of theextrusions seeks to escape to the atmosphere as the gas reaches theouter end of the extrusion passages in the pockets 58. Without thesprings 76 to retain the extrusion slugs the internal gas tends toexpand rapidly and causes the extrusions to disintegrate or sometimesrupture, as soon as the compacted material reaches the outer end of theextrusion passages. The back pressure or restriction of outward movementof the extruded material exerted by the springs 76, which are in directengagement with the extruded material, provide a physically stabilizingforce which allows the gases to escape more slowly along the length ofthe rod-like extrusions as they are exiting the outer end of theextrusion passages 52. The springs 76 while exerting back pressure onthe rod-like extrusions of solid carbon dioxide, permit vapor that isformed around the pellet during the compaction and extrusion process toescape to the atmosphere. As seen in FIG. 7, the passages 52 arecircular in cross-section at the outer end and communicate directly withthe pockets 58 which are rectangular in cross-section and this permitsthe gas to escapeat the corners defined between the circular passagesand the essentially rectangular or square cross-sections defined by thepocket walls and the outer ends of the springs.

The elongated, solid phase, carbon dioxide rod-like extrusions projectoutwardly beyond the outer free ends of the deflected springs 76 andeventually the extrusions will break off under their own weight if theyare not sooner broken off by engagement with a deflecting surface or thelike. If desired, an annular cone shaped deflector shield 77 (FIG. 1) isspaced outwardly of the outer end of the extrusion passages to limit thelength of extruded material and thereby form pellets having a selectedmaximum length. It has been observed that, if the springs are removedafter the extrusion process has been initiated, the'rod-like extrusionstend to break off or rupture into small pieces after exiting the outerend of the passages 52. This indicates that the springs 76 and thecontact back pressure exerted thereby play an important stabilizing rolein the process. It is believed that the process of extruding thematerial against the contact pressure of the springs 76 provides arestrictive, stabilizing force on the extruded material which holds thematerial together while allowing internal, vaporous carbon dioxide toescape without damage to the extruded body of material. This reduces thetendency of the material to rupture or disintegrate upon reaching theouter end of the extrusion passages 52 is reduced even though thepressure in the pockets is essentially at ambient conditions.

in accordance with the present invention, extrusion pressures in a rangeof 2600 to 3500 psia in the compacted snow are provided to form thesolid phase rodlike extrusions of carbon dioxide in the die passages 52in the wall of the extrusion chamber 30. Compaction of the snow isobtained by a generally cylindrical impeller 80, which is mounted forrotation on an eccentric segment 82 of a main drive shaft 84 driven bythe gear reducer 14. As previously indicated, the drive shaft 84 isdirectly coupled to the output shaft of the gear reducer and iscoaxially aligned therewith along the vertical axis 32 which is thecentral axis of the extrusion chamber 30 and die rings 34, 36 and 38.The impeller supporting portion 82 of the drive shaft 84 is spacedradially outward with respect to the axis 32 and parallel thereto sothat the impeller 80 orbits around the axis within the extrusion chamber30 as the main drive shaft 84 is rotated by the gear reducer and motor.

The drive shaft 84 is supported for rotation in a cylindrical housing 86having its upper end secured to the underside of the base plate 24 bysuitable means such as cap screws 88. The cylindrical shaft housing isformed with a bearing shoulder 87 adjacent the lower end and is providedwith an internal, annular groove 89 spaced downwardly therefor seating asnap ring 90 which retains a bearing ring 92 preferably of the typeincluding barrel-shaped rollers. A suitable bearing support arrangementand upper bearing (not shown) is provided adjacent the upper end of theshaft housing 86, and the upper shaft bearing provides support for theshaft 84 to prevent axial displacement thereof in the shaft housingduring rotation. An annular shaft seal 96 is provided to seal betweenthe shaft 84 and the bearing 92 adjacent the junction of the eccentricpin portion 82 and thereby prevent carbon dioxide from entering thelower end of the main shaft housing 86. The impeller 80 is formed withan enlarged axial center bore 98 larger in diameter than the outerdiameter of the eccentric spindle 82 on the main drive shaft 84 and theupper and lower ends of the bore 98 are formed with enlarged shoulders100 in order to accommodate the outer races of a pair of roller bearingrings 102 for rotatively supporting the impeller on the eccentricspindle 82. The inner races of the bearing rings are spaced apart on thespindle by a sleeve 99. The impeller 80 is retained on the eccentricshaft spindle 82 by means of a lock washer 104 and nut [06 threaded ontoa lower threaded end portion of the spindle. The enlarged shoulders 100at opposite ends of the axial bore 98 in the impeller 80 are formed inupwardly and downwardly projecting enlarged cylindrical bosses 108,which bosses provide a cylindrical curtain wall for encircling the outerraces of the bearing rings 102. An upper washer 110a seals the upperbearing ring 102 while a lower washer 11% is provided adjacent the lowerbearing ring 102 for sealing and an annular seal 112 is provided to sealbetween the lower end of the main portion of the drive shaft 84 and theupper washer 110a.

In accordance with the present invention the midlevel section of therotary impeller 80 is cylindrical and of a thickness "T" slightly lessthan the vertical spacing between a pair of opposing, annular,horizontal shoulder surfaces 114 on the upper and lower die rings 34 and38. The upper and lower shoulder surfaces 114 together with thecylindrical surfaces 54 of the middle die ring 36 and the aligned insidesurfaces 46 of the upper and lower die rings 34 and 38 provide ahorizontal annular groove or track 115 around the inside wall of theextrusion chamber 30. As the impeller orbits around the chamber, asegment of the outer periphery of the impeller penetrates into thegroove 115 to form a compression zone of crescent shape (designated bythe letter A in FIG. 3) wherein the snow is compacted and extruded outthe passages 52. The maximum penetration of the impeller into the groove115 occurs at the center of the crescent shaped compression zone A"which extends angularly on opposite sides thereof as indicated by theangles a.

Diametrically opposite the compression zone A" as viewed in FIG. 3,there is provided in the extrusion chamber 30 an open space or expansionzone labelled B, which zone is also crescent shaped and substantiallylarger than the compression zone. The expansion zone comprises asubstantial portion of the volume of the annular groove 115 and theremaining volume or space between a major segment of the outer peripheryof the impeller and the adjacent surface of the outer wall of theextrusion chamber. As viewed in FIG. 3 it will be seen that the volumeof the compression zone A" is smaller than the expansion zone B" so thatthe carbon dioxide snow may be formed by the flashing of liquid carbondioxide injected directly into the expansion zone at several spacedapart locations therein. Because of the direct injection of flashedcarbon dioxide in the extrusion chamber 30, the apparatus does notrequire a large, voluminous snow horn and does not rely on gravity feedto fill the extrusion chamber with snow. The impeller orbits to compactand compress the snow into the groove 115 and forces the material intothe entrance of the tapered extrusion passages 52. As further compactiontakes place, the compacted snow is extruded outwardly through the outer,slightly tapered section of the extrusion passages 52 until rod-likeextrusions of solid phase carbon dioxide are pushed out into the pockets58. Because a segment of the outer periphery of the impeller penetratesoutwardly into the groove between the upper and lower shoulder surfaces114, the carbon dioxide snow in the extrusion chamber 30 is entrapped inthe compression zone within the groove and is thus subjected toextremely high pressure and compaction force during extrusion outwardlythrough the tapered passages 52.

The compression zone A" moves around the extrusion chamber 30 as theimpeller 80 orbits and the leading and trailing edges of the zoneprecede and follow the edges of the larger expansion zone B" which ispartially filled with carbon dioxide snow. Each orbit of the impeller 80causes the formation of additional rodlike extrusions in the passages 52adjacent the compression zone A and the extrusion or outward push oneach rod-like member takes place intermittently rather thancontinuously. The extrusions thus grow in length intermittently eachtime the impeller 80 makes an orbit as the shaft 84 makes one completerevolution. Sealing engagement between the upper and lower an nular ringshoulder surfaces 114 of the groove 11S and the upper and lower faces ofthe mid-level portion of the impeller 80 provide the compactingentrapment of the snow in the compression zone A and this results in amobile, orbiting, localized zone of extremely high compaction pressurein the extrusion chamber 30 which followed and preceded by therelatively low pressure, larger volume expansion zone B. Flashing orexpansion of theliquid carbon dioxide into the low pressure expansionzone B in the chamber 30 develops carbon dioxide snow and this snowpartially fills the chamber. x

In accordance with the present invention the annular die rings 34, 36and 38 are supported from the lower end of the main shaft housing 86 bymeans of an outwardly extending annular flange structure I16 welded orotherwise secured on the lower end of the housing. The flange structure116 includes a horizontal, lower annularface 118 which is adapted toring against an upper face 120 on the upper die rinG 34. The flangestructure 116 provides a closure for the upper end of the annularextrusion chamber 30 and is formed with a plurality of vertical passages42 aligned to match those in the die rings for accommodating the bolts40.

on the impeller 80 and the lower end of the extension wall terminatesadjacent the level of the annular, upper shoulder surface 114 of thegroove 115.

The lower filter ring 132 is seated around its inner periphery in anannular shoulder 140 formed in an upwardly extending annular ring 142which is similar in dimension and configuration to the ring 138 formedat the lower end of the shaft housing 86. The ring 142 is adapted tocooperate with the lower, downwardly depending boss 108 on the impeller80 and is integrally fonned to extend upwardly from a circular bottomwall or closure plate 142 secure to the underside of the lower die ring38 by the bolts 40.

As best shown in FIGS. 2 and 6 the upwardly extending ring 142 forms theinside wall of a lower, annular groove or vapor exhaust manifold 146,which groove is similar in size and shape to the upper manifold orgroove 122 above the upper filter ring I32. Carbon di- In addition tothe passages 42 for the bolts'40, a single passage 42a (FIG. 2) isprovided to deliver liquid carbon dioxide from the inlet supply conduit26 into the downwardly extending aligned vertical passages 42a in therespective upper, middle and lower die rings 34, 36 and 38. I

The underside of the'flange structure I16 and the outer portion of thelower end of the tubular housing 86 are formed with an annular groove orexhaust manifold therein designated as 122 in FIGS. 2 and 4. The grooveserves as a manifold for collecting and exhausting the vaporous carbondioxide formed during the flashing and expansion process in theextrusion chamber 30 and released during the initial stages ofcompaction of the snow. The exhaust grooveis in direct communicationwith a pair of exhaust fittings 124 mounted on diametrically oppositesides of the flange structure oxidevapor formed during the flashingprocess and during initial stages of compaction in the annular extrusionchamber 30 may pass freely in an upward or downward direction from thechamber through the respective' upper and lower filter rings 132. Thisexhaust vapor is collected in the manifold grooves 122 and 146,respectively, and is delivered to the exhaust conduit 28. As viewed inFIG. 6 a circular lower closure plate 144 for the extrusion chamber 30is provided with a plurality of circumferentially spaced apart passages42 matching those of the die rings for accommodating the bolts 40 whichsecure the assembled rings 34, 36 and 38 and the closure plate with theupper flange structure 116 on the shaft housing 86.

In an embodiment constructed in accordance with the features of thepresent invention, the filter rings 116 and the fittings are connectedto elbows 126 (FIGS. 1 and 2). The elbows are connected to the exhaustconduits 28 via coupling units 128 (FIG. 1) and as illustrated in FIG.1, the pair of exhaust fittings 124 are positioned at 90 angles withrespect to and on opposite sides of the inlet supply line 26. Theexhaust linesare substantially larger in size than the supply line inorder to handle a higher volume flow rate of vapor ous carbon dioxide.The exhaust fittings 124 are threaded into apertures formed in theflange structure I16, and a pair of short passages 130 (FIG. 2) areprovided to communicate between the exhaust fittings and the uppersurface of the annular groove 122 which comprises the upper exhaustmanifold for the extrusion apparatus 12.

In order to prevent the solid carbon dioxide or snow in the extrusionchamber 30 from entering the annular exhaust manifold 122, theextrusion'assembly 12 is provided with a pair of annular filter rings132 disposed above and below the die rings 34 and 38 and adapted topermit passage of vaporous carbon dioxide while filtering out orlimiting the passage of solid phase carbon dioxide snow. The annularfilter rings 132 are seated with their outer periphery in annularrecesses or shoulders I34 formed in the die rings 34 and 38. The upperfilter ring 132 has an inner peripheral edge seated in a shoulder 136formed in a downwardly extending circular wall portion 138 formed at thelower end of the tubular shaft housing 86. The annular extension wall138 is adapted to encircle the upwardly projecting boss 108 132 wereformed of perforated stainless steel material, approximately 0.031 inchin thickness and were formed with V-shaped corrugations thereinextending generally radially around the ring with respect to the axis 32as best shown in FIG. 3. The V-shaped corrugations in the filter ringsare formed at approximately a angle with respect to the horizontal, andthe width of the corrugations enlarges toward the outer periphery of thering due to the radial orientation of the corrugations. The sheetmaterial used for the filter rings is formed with perforations ofapproximately 0.030 inch in diameter and it has been found that rings ofthis style serve well to prevent the carbon dioxide snow from passingvertically out of the annular extrusion zone in the expansion region Bas the impeller orbits. The surfaces 114 of upper and lower die rings 34and 38 shield the filter rings 132 from the pressure in the compactionzone A, because of the penetration of the impeller 1 80 within theannular groove on the inside of the die wall. The filter rings 1'32 arethus not subjected to the extremely high extrusion pressures developedfor compaction and extrusion and this feature permits a relatively lightweight filter ring structure to be utilized to effectively block theflow of solid carbon dioxide snow while permitting the ready escapepassage of vaporous carbon dioxide.

' Referring to FIGS. 2 and 4, the upper and lower edges on the outerperiphery of the mid-level section of the impeller 80 that penetratesthe groove 115 between the ring surfaces 114 is provided with sharpcomers in order to provide shearing or cutting action on the snowexpansion zone B above the upper ring surface 114 beneath the upperfilter ring 132, provides a filter medium itself for the carbon dioxidevapor moving upwardly and the filter ring 132 prevents the snow cake ofsolid phase material from passing out to exhaust. The same actionprevails in the area above the lower filter ring 132 below the lowerring surface 114 where the annular snow cake form as a lower vaporfilter and the metal filter ring 132 prevents the snow from moving intothe lower exhaust groove 146. The sharp peripheral edges of the upperand lower surfaces on mid-level section of the impeller 80 arecontinuously shearing off the surfaces of the upper and lower filtercakes to provide a clean, open entry surface for the gases escapingupwardly and downwardly from the mid-level of the extrusion chamber intothe exhaust manifold grooves 122 and 146. In this manner, plugging up orglazing over of the filter cake surfaces which engage the upper andlower surfaces of the impeller mid-section is avoided and the filtercakes of carbon dioxide snow are maintained in a condition to readilypass the vapor toward the metal filter rings.

The passages 42 in the bottom closure plate 144 extend completelythrough the plate so that nuts and washers may be provided on the lowerend of the bolts 40 to secure the die rings, flange structure and platetogether. The passages 42 in the flange structure 116, the die rings 34,36 and 38 and the bottom closure plate 144 are aligned to match oneanother and the liquid carbon dioxide inlet passage 42a in the dieringsis adapted to communicate with a passage 42a formed in the bottomclosure plate 144 which terminates short of the lower surface thereof.Similarly, the distribution passages 42b in the lower die 38 is adaptedto communicate with four passages 42b formed in the bottom closure plate144 spaced 90 apart and terminating short of the lower surface of theplate.

In order that the exhaust vapor collected in the lower groove ormanifold 146 may flow upwardly into the upper groove or manifold 122through selected ones of the passages 42 in the die rings which do notcontain bolts 40, the bottom closure plate 144 is formed with aplurality of fingerlike, radially outwardly extending recesses 42c forpassing the vapor collected in the groove 146 to the lower open ends ofthe aligned open passages 42 in the die rings. Similar finger-shapedgrooves 42c are provided in the flange structure 116 to bring the gasesradially inward into the upper collecting manifold or groove 122 forexhaust. From the foregoing description it will be seen that the novelstructures assembled together to form the annular extrusion chamber 30including the flange structure 116, the die rings 34, 36 and 38, and thebottom closure plate 144 provide a unique system for directing the flowof liquid and gaseous carbon dioxide to desired locations.

Liquid carbon dioxide from the line 26 flows downwardly through alignedpassages 42a in the flange structure 116, the die rings 34, 36 and 38and into the passage 42a in the bottom closure plate 144. From thispoint the liquid flows radially inwardly via a passage 148 whichterminates in a port 150 on the underside of the bottom closure plate.

Liquid carbon dioxide which is to be injected into the annular extrusionchamber 30 in synchronism with the orbiting movement of the impeller 80is distributed into selected ones of four, quadrantally spaced ports 152provided on the lower surface of the bottom closure plate. The ports 152are positioned at the inner ends of radially outwardly extendingdistribution passages 154 arranged at angles to one another andterminating at their outer ends in communication with the closed lowerends of the vertical passages 42b. Liquid from the ports 152 flowsupwardly through the aligned passages 42b in the lower die ring 38, forinjection into the expansion zone B ahead and behind the compressionzone A of the orbiting impeller.

In order to synchronize the injection of liquid carbon dioxide with theposition and movement of the orbiting impeller 80 around the annularextrusion chamber 30, the apparatus 12 includes a distributor assembly156 (FIG. 2) which comprises an upper distributor plate 158 and a lowervalve housing 160, both secured in coaxial alignment with the centralaxis 32 of the extrusion apparatus. The distributor plate is formed witha vertical passage 162 adapted to communicate with the port on theunderside of the bottom closure plate 144, as best shown in FIGS. 2 and6 and the passage 162 terminates short of the underside of thedistributor plate 158. The passage 162 is in communication with theouter end of a radially inwardly extending horizontal feed passage 164which is in communication at its inner end with a downwardly extendingvertical passage 166 for directing fluid downwardly into an annularvalve chamber 168 formed in the valve housing 160 (FIGS. 2 and 5).

Liquid carbon dioxide at the desired supply pressure of approximately210 to 250 psia is supplied to the extrusion apparatus 12 via the inletline 26 and flows downwardly through the aligned vertical passages 42ain the flange structure 116 and the die rings 34, 36 and 38 into thepassage 42a in the bottom closure plate 144. The liquid is then directedradially inwardly via the passage 148 and then downwardly through theport 150 and passage 162 in the valve plate 158. The liquid flowsradially inwardly in a horizontal path through the passage 164 and thendownwardly through the vertical passage 166 to fill the valve chamber168 formed inside the valve housing 160.

In accordance with the present invention a valve rotor assembly 170comprising an upper rotor disk 172 and interconnected shaft 174 ismounted for rotation in coaxial alignment with the main shaft axis 32.The valve rotor shaft is supported by a pair of bearings 176 mounted ina vertical bore 178 formed at the center of the distributor plate 158.The valve rotor is driven in synchronism with the impeller 80 by meansof a short, downwardly extending spindle extension 180 formed on thelower end of eccentric spindle 82 of the main drive shaft 84. Thespindle extension projects downwardly in driving engagement with thedish 172 into a radial slot 172a formed in the outer edge of the disk.As the spindle 82 of the drive shaft 84 orbits, the valve rotor 170 isdriven in synchronism therewith. The lower end of the valve shaft 174extends downwardly into the valve chamber 168 and a disk 182 is keyed torotate with the shaft by means of a conventional Woodruf type key 184.The disk 182 is drivingly interconnected with a rotating valve member186 mounted on the shaft 174 and biased upwardly against a smooth faceon the underside of the distributor plate 158 by means of a helicalspring 188 coiled around a lower end portion of the shaft. The spring issecured between the lower face of the disk 182 and the upper face of aretaining washer 190 by a cap screw or equivalent 192 threaded into thelower end of the rotor shaft 174.

The valve member 186 and drive disk 182 are drivingly interconnected toeach other by an eccentric drive pin 194 as best shown in FIG. so thatin normal operation, the valve member 186 is keyed to rotate insynchronism with the rotative position of the impeller 80 and thecompression zone A."

In accordance with the present invention, the liquid carbon dioxidewhich flows into the valve chamber 168 is distributed both ahead of andbehind the compression zone A as the impeller orbits around the annularextrusion chamber 30 and the distribution of liquid is controlled bymeans of the valve member 186. As shown in FIG. 5 the valve 186 includesa large radius, port closing, peripheral portion or land, which includesa segment occupying approximately 180 of its periphery, and a smallradius, port opening, section occupying the remaining 180 of periphery.The liquid carbon dioxide in the valve chamber 168 is controlled to flowupwardly through four equilaterally spaced ports 196 opening on thelower face of the valve distributor plate 158 as best shown in FIG. 2and these ports are spaced 90 apart at a radius less thanthat of thevalve closing land portion of the valve 186 but greater than the radiusof the valve opening section of the valve. Because there are fourequilaterally spaced distribution ports '196 that are controlled by therotating valve 186, and

because the valve opening segment occupies half of the total periphery,at any given time two ports will be open for the distribution of fluidto the extrusion chamber 30 and two ports will be closed. This meansliquid will flow to the chamber through only two of the four availablepassages 4212 at any given instant. The four distribution ports 196 arein communication with the inner ends of a plurality of radiallyoutwardly extending horizontal passages 198 in the, valve distributorplate 158 and these passages are arranged with 90 angular spacingbetween them around the axis 32. The outer ends of the passages 198 arein communication with vertical passages 200, the upper ends of which arein communication with the ports 152. The ports 152 are in communicationwith the inner ends of the radial distribution passages 154, which inturn communicate with the four, quadrantally spaced, verticaldistribution passages 42b formed in the bottom closure plate 144 andaligned with the passages 42b in the die ring 38.

The flow of liquid carbon dioxide is thus directed into the valvechamber 168 and is distributed by the valve 186 to flow out through onlytwo of the four radial distribution passages 198 and 154 which lead tothe four vertical passages 42b in the die ring 38. Which ones of thepassages are being supplied with fluid is dependent upon the preciseposition of the orbiting impeller 80 and the valve 186 which is keyed torotate in synchronism therewith.

Liquid carbon dioxide is flashed into the chamber 30 in advance of andbehind the compression zone A into the larger expansion zone B." Theimpeller 80 and orbiting radius thereof are dimensioned so that thecompression zone A occupies a smaller, angular range (for'exampleapproximately 48 on either side of the point of maximum compression orpenetration of the impeller into the groove or track 115) than does thelarger expansion zone B and fluid is only injected into'the expansionzone.

In accordance with the present invention the lower die ring 38 isprovided with four radially inwardly directed, horizontal injectionpassages 202 (FIG. 4),

which passages are in communication with the vertical passages 42b.Within each of these passages there is mounted an injection nozzlestructure 204 comprising a hollow tubular body including an enlargedouter end portion having external threads thereon for threadedengagement within an enlarged outer end portion of the passages 202outboard of the vertical passages 42b.

The hollow tubular body of the nozzle structures 204 are formed withopenings 206 adjacent the outer end forpermitting the fluid in thepassages 42b to enter the nozzles. The fluid enters the injectionnozzles adjacent the outer end through the openings 206 and is directedradially inwardly through the hollow body of the nozzles towards theinner end. The inner ends are closed by end plugs 208 (FIG. 4) and eachnozzle is provided with a discharge orifice 210 adapted to flash thehigh pressure liquid carbon dioxide into the low pressure expansion zoneB in the upward direction as shown by the arrows C (FIGS. 4 and 2). Theouter end portions of the nozzle structure 204 are identified so thatwhen inserted in the bores 202 the nozzles may be properly orientated sothat the orifices 210 will discharge upwardly as shown in the drawings.As previously described only two of the nozzles will be flashing liquidcarbon dioxide into the crescent shaped expansion zone B at any giveninstant to fill the expansion zone with carbon dioxide snow.

As the impeller orbits, the valve 186 controls the flow to the nozzles204 which are spaced quadrantally around the annular extrusion chamber30. The crescent shaped expansion zone B is continuously being chargedwith carbon dioxide snow flashed from the discharge orifices 210 of theinjection nozzles 204. Liquid carbon dioxide is supplied to theextrusion apparatus 12 at an operating pressure range of approximately210 to 250 psia. As this liquid is flashed via the nozzle orifices 210into the expansion zone B ahead of and behind the moving compressionzone A defined by the impeller, the pressure is rapidly reduced asexpansion occurs. The material passes through the triple point and amixture of snow and vapor results at a pressure slightly above oneatmosphere. As the compression zone A orbits aroundthe annular extrusionchambers 30, the snow is compacted and the pressure is raised rapidly asthe snow enters the extrusion passages 52. As the compacted snow isforced outwardly through the extrusion passages 52 the pressure gradientdrops toward ambient pressure conditions at the outer end at slightlyabove atmospheric as the material exits the extrusion passages into thepockets 58. This pressure drop occurs rapidly in the extrusion processbut is intermittent as previously described. A slight amount of pressureincrease is shown by the stabilizing contact back pressure exerted onthe rod-like extrusions by the outer free ends of the springs 76. Thisslight increase in pressure by the springs 76 results in a stableextrusion of solid phase carbon dioxide.

Although the present invention has been described with reference to asingle illustrative embodiment thereof, it should be understood thatnumerous other modifications and embodiments can be devised by thoseskilled in the art that will fall within the spirit and scope of theprinciples of this invention.

What is claimed as new and desired to be secured by letters Patent ofthe United States is:

1. Apparatus for making compacted pellets of solid phase carbon dioxidecomprising die means having at least one extrusion passage with an innerend and an outer end injector, means for flashing liquid carbon dioxideinto snow adjacent said inner end of said passage; compression means forcompacting and extruding said snow through the inner end of said passageto form elongated rod-like extrusions passing out of said outer end ofsaid passage; and back pressure means for exerting contact pressureagainst said extrusions exiting the outer end of said passage.

2. The apparatus of claim 1 wherein said last mentioned means comprisesa deflectable spring normally closing the outer end of said extrusionpassage, said spring being deflectable by said rod-like extrusions ofsolid phase carbon dioxide moving outwardly of the outer end of saidextrusion passage.

3. The apparatus of claim 2 wherein said spring comprises a strip ofmaterial having a deflectable free end positioned to extend across saidouter end of said extrusion passage and means for supporting said stripfrom said die means away from said free end.

4. The apparatus of claim 3 wherein said die means includes at least onepair of adjacent, spaced apart, extrusion passages, said spring stripcomprising a generally U-shaped member having opposite free endsextending across the outer ends of said passages and deflectableinwardly toward one another by said rod-like extrusions as they areextruded out through said passages, said means for supporting said stripcomprising pin means between said outer ends of said passages engaging amiddle bight portion of said U-shaped memher.

5. The apparatus of claim 2 wherein said die means comprises an annularwall having a plurality of radially extending extrusion passagestherein, said compression means comprising an impeller mounted fororbital movement around the interior of said annular wall for compactingsaid snow and extruding it out through said radial extrusion passagesagainst the back pressure of said deflectable spring.

6. The apparatus of claim 5 wherein said injector means comprises aplurality of spray nozzles positioned at spaced apart locations aroundthe interior of said annular wall for flashing liquid carbon dioxideinto snow in an area between said impeller and the inner ends of saidextrusion passages.

7. The apparatus of claim 6 including valve means operative in responseto the relative eccentric position of said impeller and said annularwall of said die means for closing off the flow of liquid carbon dioxideto one of said spray nozzles while opening the flow to another spraynozzle.

8. The apparatus of claim 6 wherein said annular wall of said die meansis formed with an annular groove in communication with the inner ends ofsaid extrusion passages for receiving a portion of the periphery of saidimpeller, said portion of said impeller received within said groove andthe wall surfaces of said groove defining a compression zone movablearound said die as said impeller orbits.

9. The apparatus of claim 8 including valve means operative to controlthe flow of liquid carbon dioxide to said spray nozzles for supplyingnozzles positioned ahead of said compression zone and for shutting offthe supply to nozzles in said zone.

10. Apparatus for making compacted pellets of solid 5 phase carbondioxide comprising an extrusion chamber having an outer wall formed byannular die means having a plurality of extrusion passages extendingoutwardly ofa central axis between inside and outside sur faces thereof;impeller means mounted in said chamber for orbital movement around saidaxis to form a moving compression zone adjacent a segment of saidannular die means for extrusion of carbon dioxide through said passagesand an open zone ahead of said compression zone in the path thereof; andinjection means for flashing liquid carbon dioxide into said open zoneforming snow to be compressed and extruded into rod-like extrusions ofsolid phase carbon dioxide by said impeller moving around said die meansin said extrusion zone.

11. The apparatus of claim 10 wherein said injection means comprises aplurality of spray nozzles positioned at radially spaced apart locationsaround the inside surface of said annular die wall and valve meansresponsive to the position of said compression zone in said annular diewall for supplying liquid carbon dioxide to said nozzles in said openzone and shutting of the supply to a nozzle adjacent said compressionzone.

12. The apparatus of claim 11 wherein said annular die wall is formedwith a groove around the inside surface thereof in communication withthe inside ends of said extrusion passages, said groove having opposedparallel circular side surfaces engaging opposite sides of said impellerin said compression zone.

13. The apparatus of claim 12 wherein said spray nozzles are spacedinwardly of said side surfaces of said groove in said die wall towardsaid axis for directing a spray between an outer periphery of saidimpeller and said inside surface of said die wall.

14. The apparatus of claim 13 including a vapor exhaust means forremoving carbon dioxide vapor from said chamber, said exhaust meanscomprising an annular exhaust channel around at least one side of saidextrusion chamber inwardly of said side surfaces of said groove in saiddie wall and an annular filter between said extrusion chamber and saidexhaust channel for passing gases and containing solid carbon dioxide.

'15. The apparatus of claim 14 wherein said vapor exhaust means includesa pair of said annular exhaust channels on opposite sides of saidextrusion chamber and a pair of said annular filters, and a plurality ofexhaust passages in said die wall for interconnecting said annularexhaust channels.

16. The apparatus of claim 15 wherein said exhaust passages are normalto and radially spaced between adjacent extrusion passages in said diewall.

17. The apparatus of claim 15 including spray nozzles in said extrusionchamber for flashing sprays of liquid carbon dioxide into snow betweenthe periphery of said impeller and said annular groove in said die wall.

18. The apparatus of claim ll wherein said valve means includes aplurality of supply passages for supplying liquid carbon dioxide to saidspray nozzles and a rotor movable to alternately open and close saidsupply passages driven in synchronism with said orbiting impeller.

19. The apparatus of claim 18 including eccentric drive means drivinglyinterconnecting said impeller and said valve rotor.

2. The apparatus of claim 1 wherein said last mentioned means comprisesa deflectable spring normally closing the outer end of said extrusionpassage, said spring being deflectable by said rod-like extrusions ofsolid phase carbon dioxide moving outwardly of the outer end of saidextrusion passage.
 3. The apparatus of claim 2 wherein said springcomprises a strip of material having a deflectable free end positionedto extend across said outer end of said extrusion passage and means forsupporting said strip from said die means away from said free end. 4.The apparatus of claim 3 wherein said die means includes at least onepair of adjacent, spaced apart, extrusion passages, said spring stripcomprising a generally U-shaped member having opposite free endsextending across the outer ends of said passages and deflectableinwardly toward one another by said rod-like extrusions as they areextruded out through said passages, said means for supporting said stripcomprising pin means between said outer ends of said passages engaging amiddle bight portion of said U-shaped member.
 5. The apparatus of claim2 wherein said die means comprises an annular wall having a plurality ofradially extending extrusion passages therein, said compression meanscomprising an impeller mounted for orbital movement around the interiorof said annular wall for compacting said snow and extruding it outthrough said radial extrusion passages against the back pressure of saiddeflectable spring.
 6. The apparatus of claim 5 wherein said injectormeans comprises a plurality of spray nozzles positioned at spaced apartlocations around the interior of said annular wall for flashing liquidcarbon dioxide into snow in an area between said impeller and the innerends of said extrusion passages.
 7. The apparatus of claim 6 includingvalve means operative in response to the relative eccentric position ofsaid impeller and said annular wall of said die means for closing offthe flow of liquid carbon dioxide to one of said spray nozzles whileopening the flow to another spray nozzle.
 8. The apparatus of claim 6wherein said annular wall of said die means is formed with an annulargroove in communication with the inner ends of said extrusion passagesfor receiving a portion of the periphery of said impeller, said portionof said impeller received within said groove and the wall surfaces ofsaid groove defining a compression zone movable around said die as saidimpeller orbits.
 9. The apparatus of claim 8 including valve meansoperative to control the flow of liquid carbon dioxide to said spraynozzles for supplying nozzles positioned ahead of said compression zoneand for shutting off the supply to nozzles in said zone.
 10. Apparatusfor making compacted pellets of solid phase carbon dioxide comprising anextrusion chamber having an outer wall formed by annular die meanshaving a plurality of extrusion passages extending outwardly of acentral axis between inside and outside surfaces thereof; impeller meansmounted in said chamber for orbital movement around said axis to form amoving compression zone adjacent a segment of said annular die means forextrusion of carbon dioxide through said passages and an open zone aheadof said compression zone in the path thereof; and injection means forflashing liquid carbon dioxide into said open zone forming snow to becompressed and extruded into rod-like extrusions of solid phase carbondioxide by said impeller moving around said die means in said extrusionzone.
 11. The apparatus of claim 10 wherein said injection meanscomprises a plurality of spray nozzles positioned at radially spacedapart locations around the inside surface of said annular die wall andvalve means responsive to the position of said compression zone in saidannular die wall for supplying liquid carbon dioxide to said nozzles insaid open zone and shutting of the supply to a nozzle adjacent saidcompression zone.
 12. The apparatus of claim 11 wherein said annular diewall is formed with a groove around the inside surface thereof incommunication with the inside ends of said extrusion passages, saidgroove having opposed parallel circular side surfaces engaging oppositesides of said impeller in said compression zone.
 13. The apparatus ofclaim 12 wherein said spray nozzles are spaced inwardly of said sidesurfaces of said groove in said die wall toward said axis for directinga spray between an outer periphery of said impeller and said insidesurface of said die wall.
 14. The apparatus of claim 13 including avapor exhaust means for removing carbon dioxide vapor from said chamber,said exhaust means comprising an annular exhaust channel around at leastone side of said extrusion chamber inwardly of said side surfaces ofsaid groove in said die wall and an annular filter between saidextrusion chamber and said exhaust channel for passing gases andcontaining solid carbon dioxide.
 15. The apparatus of claim 14 whereinsaid vapor exhaust means includes a pair of said annular exhaustchannels on opposite sides of said extrusion chamber and a pair of saidannular filters, and a plurality of exhaust passages in said die wallfor interconnecting said annular exhaust channels.
 16. The apparatus ofclaim 15 wherein said exhaust passages are normal to and radially spacedbetween adjacent extrusion passages in said die wall.
 17. The apparatusof claim 15 including spray nozzles in said extrusion chamber forflashing sprays of liquid carbon dioxide into snow between the peripheryof said impeller and said annular groove in said die wall.
 18. Theapparatus of claim 11 wherein said valve means includes a plurality ofsupply passages for supplying liquid carbon dioxide to said spraynozzles and a rotor movable to alternately open and close said supplypassages driven in synchronism with said orbiting impeller.
 19. Theapparatus of claim 18 including eccentric drive means drivinglyinterconnecting said impeller and said valve rotor.